Layer-2 link-state protocols such as Fabricpath and TRansparent Interconnection of Lots of Links (TRILL) networks—are currently being deployed as the networking fabric to enable large scale data centers. TRILL is an IETF (Internet Engineering Task Force) protocol implemented by devices such as Routing Bridges. TRILL introduces new data and control planes for Ethernet networks. FabricPath protocol allows combining the plug-and-play simplicity of Ethernet with the reliability and scalability of Layer 3 routing. FabricPath allows for the creation of highly scalable Layer 2 multipath networks without the Spanning Tree Protocol. Such networks are used, for example, with large virtualization deployments, private clouds, and high-performance computing (HPC) environments.
TRILL proposes to use a “link-state” style routing framework by building layer-3 style “adjacencies” with physical neighbors, by sending HELLO packets. However, there is a key difference in how adjacencies are formed in TRILL and FabricPath. In FabricPath, only “point-to-point” neighbor links are allowed. However, TRILL allows LAN-based adjacencies in addition to “point-to-point”. In order to deploy LAN-based adjacencies, it should be ensured that there is only one appointed forwarder for each VLAN. The appointed forwarder for each VLAN may be responsible for the encapsulation and decapsulation of the packets belonging to each respective VLAN.
The appointed forwarder appointment process may be a centralized process for each LAN. In TRILL, the process may be performed by a designated routing bridge on a given LAN. There is no prescribed algorithm for these appointments, and prior art approaches may be somewhat naïve. One such prior art approach assigns each node on a VLAN based on simple load-sharing logic. For example, if there are V VLANs on a LAN and there are N routing-bridges on the same LAN, then each routing bridge may be appointed as an appointed forwarder for V/N VLANs.
The problem with such prior art approaches is that these fail to consider the existing appointed forwarder appointments. This may result in traffic disruption for a large number of VLANs due to the change of the appointed forwarder.